Method of operating a micromechanical device that contains anti-stiction gas-phase lubricant

ABSTRACT

One embodiment of an micromechanical device includes a first contact surface, a moveable component having a second contact surface, and a coating of liquid or solid lubricant on at least one of the contact surfaces, where the second contact surface interacts with the first contact surface during device operation, and a gas-phase lubricant is disposed between the first contact surface and the second contact surface, where the gas-phase lubricant is adapted to increase the usable lifetime of the liquid or solid lubricant coating on the contact surfaces. One advantage of the disclosed device is that a gas-phase lubricant has a high diffusion rate and, therefore, is self-replenishing, meaning that it can quickly move back into a contact region after being physically displaced from the region by the contacting surfaces of the device during operation. Consequently, the gas-phase lubricant used with conventional solid or liquid lubricants is more reliable than solid or liquid lubricants used alone in preventing stiction-related device failures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/389,423, filed Mar. 24, 2006, which is a continuation of U.S. patentapplication Ser. No. 11/315,920, filed Dec. 22, 2005, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 60/738,730,filed Nov. 23, 2005, all of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate generally tomicro-electro-mechanical and nano-electro-mechanical systems and morespecifically to an anti-stiction gas-phase lubricant for such systems.

2. Description of the Related Art

As is well-known, atomic level and microscopic level forces betweendevice components become far more critical as devices become smaller.Micromechanical devices, such as Micro-electro-mechanical systems (MEMS)and nano-electro-mechanical systems (NEMS) is area where problemsrelated to these types of forces are quite prevalent. In particular,“stiction” forces created between moving parts that come into contactwith one another, either intentionally or accidentally, during operationare a common problem with micromechanical devices. Stiction-typefailures occur when the interfacial attraction forces created betweenmoving parts that come into contact with one another exceed restoringforces. As a result, the surfaces of these parts either permanently ortemporarily adhere to each other, causing device failure or malfunction.Stiction forces are complex surface phenomena that generally includecapillary forces, Van der Waal's forces and electrostatic attractionforces. As used herein, the term “contact” refers generally to anyinteraction between two surfaces and is not limited to the actualphysical touching of the surfaces. Some examples of typicalmicromechanical devices are RF switches, optical modulators, microgears,accelerometers, worm gears, transducers, fluid nozzles, gyroscopes, andother similar devices or actuators.

The stiction issue is especially problematic in devices such as the RFswitch, optical modulator, microgears, and other actuators. Variouselements in these devices often interact with each other duringoperation at frequencies between a few hertz (Hz) and about a fewgigahertz (GHz). Various analyses have shown that, without adding someform of lubrication to these types of devices to reduce stiction betweencomponent surfaces, product lifetimes may range from only a few contactsto a few thousand contacts, which is generally well below a commerciallyviable lifetime. Consequently, one of the biggest challenges facing theMEMS and NEMS industries is the long-term reliability of contactingmicrostructures in the face of stiction.

Several techniques to address the stiction between two contactingsurfaces have been discussed in the various publications. Thesetechniques include texturing the surfaces (e.g., micro patterning orlaser patterning) to reduce the overall adhesion force by reducing theeffective contact area, and selecting specific materials from which thecontacting surfaces are made to lower the surface energy, reducecharging, or contact potential difference between components.

Moreover, some prior references have suggested the insertion of a“lubricant” into the region around the interacting devices to reduce thechance of stiction-type failures. Such a lubricant often times is in asolid or liquid state, depending on the properties of the material, andthe temperature and pressure or environment in which the lubricant isplaced. In general, the terms a “solid” lubricant or a “liquid”lubricant is a lubricant that is in a solid or liquid state underambient conditions, which is typically defined as room temperate andatmospheric pressure. Some prior art references describe a lubricant asbeing in a “vapor” state. These references use of the term vapor phaselubricant to generally describe a mixture of components that contain acarrier gas (e.g., nitrogen) and a vaporized second component that is asolid or liquid at temperatures and pressures near ambient conditions(e.g., STP). In most conventional applications the solid or liquidlubricant will remain in a solid or liquid state at temperatures muchhigher than room temperature and pressures much lower than atmosphericpressure conditions.

Another common approach to combat stiction between interactingcomponents is to coat the various interacting components with alow-surface energy organic passivation layer, such as the self-assembledmonolayer (SAM). The low-surface energy organic passivation layercoating results in a hydrophobic surface that is used to reduce oreliminate capillary forces, molecular bonding forces, and reduceelectro-static attraction forces in some cases. The material(s) used toform a SAM layers are typically liquids under ambient conditions.Self-assembled-monolayer coatings are commonly applied to MEMS typedevices by immersion of the device in a liquid containing the componentsused to form the SAM molecules. In some cases low-surface energy organicpassivation layer, such as a SAM coating, can be formed by exposing thesurface of the device to a vapor containing a carrier gas that has SAMlayer forming components entrained in it typically by bubbling thecarrier gas through a vessel containing heated SAM layer formingcomponents. The process of forming the low-surface energy organicpassivation layer is commonly referred to in the art as “vaporlubricant.”

Typically, the low-surface energy organic passivation layer, such as SAMcoatings, are only one monolayer thick, although coatings that are a fewmonolayers have also been reported. Generally, these types of coatingshave a very limited usable lifetime, since they are easily damaged ordisplaced due to impact or wear created by the interaction of thevarious moving components. Without some way to reliably restore orrepair the damaged coatings, stiction inevitably returns, and devicefailure results. Another approach is to introduce liquid-type lubricantswithin the MEMS or NEMS package in an effort to coat contacting surfacesand reduce stiction. However, these lubricants typically diffuse awayfrom or are physically displaced during normal device operation andoftentimes diffuse too slowly to reliably cover the exposed regions toreliably prevent stiction failures. Another common problem is thatliquid lubricants tend to break down during device operation to thepoint where they no longer provide proper lubrication. Therefore, liquidlubricants must be continually replenished during device operation. Onemethod for providing lubrication to a MEMS device using a liquidlubricant is to provide a reversibly absorbing getter material withinthe package in which the MEMS device resides. This configuration isdisclosed in U.S. Pat. No. 6,843,936. This requirement introduces a hostof problems related to providing reliable supplies of such lubricants.However, adding the reversibly absorbing getter, or reservoirs, toretain the liquid lubricants increases package size and packagingcomplexity and adds steps to the fabrication process, thus increasingpiece-part cost as well as the overall manufacturing cost of MEMS orNEMS devices. Forming a device that uses these techniques will generallyrequire a number of labor intensive and costly processing steps, such asmixing the getter material, applying the getter material to the devicecontaining package, curing the getter material, conditioning oractivating the getter material, and then sealing the MEMS device and thegetter within the sealed package.

Another common approach to combat stiction between interactingcomponents is to use a nebulization process that uses a liquidlubrication system that creates a lubricant “fog,” or lubricant “mist,”that lubricates the surfaces of the MEMS device by exposing theinteracting surfaces to tiny droplets of the liquid lubricant that issuspended in a carrier gas. One such process is described in column 3,line 28 of U.S. Pat. No. 6,921,680, where it notes that “it is criticalthat the nebulizer system be maintained in a homogenous cloud of thelubricant around the device specimen.” These types of systems requireadditional steps to keep the concentration of the liquid droplets withinthe lubricant “fog” homogeneous which can be complex and costly. The useof the lubricant “fog” will also require additional processing time tolubricate the devices to ensure that the “mist” reaches all parts of adevice to form a suitable lubrication layer.

Examples of typical lubricants that are solid or liquid at ambientconditions and temperatures well above ambient temperature can be foundin reference such as U.S. Pat. No. 6,930,367. Such prior art lubricantsinclude dichlordimethylsilane (“DDMS”), octadecyltrichlorsilane (“OTS”),perfluoroctyltrichlorsilane (“PFOTCS”), perfluorodecanoic acid (“PFDA”),perfluorodecyl-trichlorosilane (“FDTS”), perfluoro polyether (“PFPE”)and/or fluoroalkylsilane (“FOTS”) that are deposited on variousinteracting components by use of a vapor deposition process, such asatmospheric chemical vapor deposition (APCVD), low pressure chemicalvapor deposition (LPCVD), plasma enhanced chemical vapor deposition(PECVD), or other similar deposition processes.

As the foregoing illustrates, what is needed in the art a more reliableand cost-effective approach to providing anti-stiction lubrication toMEMS and NEMS.

SUMMARY OF THE INVENTION

One embodiment of the invention sets forth a method of operating amicromechanical device comprising biasing one or more electrodes,wherein biasing the one or more electrodes causes a moveable componenthaving a first contact surface to interact with a second contactsurface, biasing the one or more electrodes repeatedly until a stictionforce prevents the first contact surface from being separated from thesecond contact surface, and separating the first contact surface fromthe second contact surface by exposing the first and second contactsurfaces to a gas-phase lubricant.

Embodiments of the invention may further provide a method of operating amicromechanical device comprising providing a micromechanical devicethat comprises a first contact surface, a moveable component having asecond contact surface, wherein the second contact surface interactswith the first contact surface during device operation, and a liquid orsolid lubricant material disposed on at least one of the first contactsurface and the second contact surface, causing the second contactsurface of the moveable component to interact repeatedly with the firstcontact surface, and disposing a gas-phase lubricant between the firstcontact surface and the second contact surface, wherein the gas-phaselubricant is adapted to increase the usable lifetime of the liquid orsolid lubricant.

In another embodiment, a method is provided for operating amicromechanical device that includes a moveable component having amoving surface that interacts with a fixed surface of themicromechanical device, and a liquid or solid lubricant material isdisposed on at least one of the moving surface and the fixed surface,the method comprising causing the moving surface to interact repeatedlywith the first contact surface, and disposing a gas-phase lubricantbetween the moving surface and the fixed surface, wherein the gas-phaselubricant is adapted to increase the usable lifetime of the liquid orsolid lubricant.

One advantage of the disclosed micromechanical device is that agas-phase lubricant diffuses at a substantially higher rate thanconventional solid or liquid lubricants. A higher diffusion rate enablesa gas-phase lubricant to be self-replenishing, meaning that thegas-phase lubricant can quickly move back into a contact region afterbeing physically displaced from the region by the contacting surfaces ofthe electro-mechanical device during operation. Consequently, thegas-phase lubricant more reliably prevents stiction-related devicefailures relative to conventional solid or liquid lubricants.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A schematically illustrates a cross-sectional view of a singlemirror assembly 101 according to this invention;

FIG. 1B schematically illustrates a cross-sectional view of a singlemirror assembly 101 in a deflected state, according to one embodiment ofthe invention;

FIG. 2A illustrates a close-up cross-sectional view of a single mirrorassembly 101, according to one embodiment of the invention;

FIG. 2B illustrates a close-up cross-sectional view of a single mirrorassembly 101, according to one embodiment of the invention;

FIG. 3A illustrates a close-up cross-sectional view of a single mirrorassembly 101, according to one embodiment of the invention;

FIG. 3B illustrates a close-up cross-sectional view of a single mirrorassembly 101, according to one embodiment of the invention;

FIG. 3C illustrates a close-up cross-sectional view of a single mirrorassembly 101, according to one embodiment of the invention;

FIG. 4A schematically illustrates a cross-sectional view of a singlemirror assembly 101 according to this invention;

FIG. 4B schematically illustrates a cross-sectional view of a singlemirror assembly 101 in a deflected state, according to one embodiment ofthe invention;

FIG. 4C schematically illustrates a cross-sectional view of a singlemirror assembly 101 according to this invention;

FIG. 4D schematically illustrates a cross-sectional view of a singlemirror assembly 101 in a deflected state, according to one embodiment ofthe invention;

FIG. 5A schematically illustrates a cross-sectional view of an improvedpixel device according to this invention;

FIG. 5B schematically illustrates a cross-sectional view of an improvedpixel device in a deflected state, according to one embodiment of theinvention;

FIG. 5C schematically illustrates a cross-sectional view of an improvedMEMS moveable mirror device according to this invention;

FIG. 5D schematically illustrates a cross-sectional view of an improvedMEMS moveable mirror device in a deflected state, according to oneembodiment of the invention;

FIG. 6 illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 7A illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 7B illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 7C illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 7D illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 8A illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 8B illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 8C illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 8D illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 8E illustrates a cross-sectional view of a device package assembly,according to one embodiment of the invention;

FIG. 9 illustrates a series of method steps for forming a device packageassembly, according to one embodiment of the invention;

FIG. 10 illustrates a series of method steps for forming a devicepackage assembly, according to one embodiment of the invention;

FIG. 11A illustrates a cross-sectional view of a device packageassembly, according to one embodiment of the invention;

FIG. 11B illustrates a cross-sectional view of a device packageassembly, according to one embodiment of the invention;

FIG. 12 illustrates a cross-sectional view of a device package assembly,according to another embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to a device thathas an improved usable lifetime due to the addition of a gas-phaselubricant that reduces the likelihood of stiction occurring between thevarious moving parts in an electromechanical device. In one example,aspects of this invention may be especially useful for fabricating andusing micromechanical devices, such as MEMS devices, NEMS devices, orother similar thermal or fluidic devices. In general, a gas-phaselubricant is disposed around components of such devices that interactwith one another during operation to reduce the chances ofstiction-related failures. One of skill in the art will recognize thatthe term lubricant, as used herein, is intended to describe a materialadapted to provide lubrication, anti-stiction, and/or anti-wearproperties. As described in further detail herein, the term gas-phaselubricant as used herein is generally intended to describe a lubricantthat is in a gaseous state at all times during the operation and storageof a device.

FIG. 1A illustrates a representative micromechanical device that is usedherein to describe various embodiments of the invention. The deviceshown in FIG. 1A is intended to schematically illustrate across-sectional view of a single MEMS device, such as a single mirrorassembly 101 contained in a spatial light modulator (SLM). Typically, aMEMS device contains one or more moving parts that contacts or interactswith one or more surfaces found in the device during device operation.One should note that the MEMS device shown in FIG. 1A is not intended inany way to limit the scope of the invention described herein, since oneskilled in the art would appreciate that the various embodimentsdescribed herein could be used in other MEMS, NEMS, larger scaleactuators or sensors, or other comparable devices that experiencestiction or other similarly related problems. While the discussion belowspecifically discusses the application of one or more of the variousembodiments of the invention using a MEMS or NEMS type of device, theseconfigurations are not intended to be limiting as to the scope of theinvention.

In general, a single mirror assembly 101 may contain a mirror 102, base103, and a flexible member 107 that connects the mirror 102 to the base103. The base 103 is generally provided with at least one electrode(elements 106A or 106B) formed on a surface 105 of the base 103. Thebase 103 can be made of any suitable material that is generallymechanically stable and can be formed using typical semiconductorprocessing techniques. In one aspect, the base 103 is formed from asemiconductor material, such as a silicon containing material, andprocessed according to semiconductor processing techniques. Othermaterials may be used in alternative embodiments of the invention. Theelectrodes 106A, 106B can be made of any materials that conductelectricity. In one aspect, the electrodes 106A, 106B are made of ametal (e.g., aluminum, titanium) preferentially deposited on the surface105 of the base 103. A MEMS device of this type is described in thecommonly assigned U.S. patent application Ser. No. 10/901,706, filedJul. 28, 2004.

The mirror 102 generally contains a reflective surface 102A and a mirrorbase 102B. The reflective surface 102A is generally formed by depositinga metal layer, such as aluminum or other suitable material, on themirror base 102B. The mirror 102 is attached to the base 103 by aflexible member 107. In one aspect, the flexible member 107 is acantilever spring that is adapted to bend in response to an appliedforce and to subsequently return to its original shape after removal ofthe applied force. In one embodiment, the base 103 is fabricated from afirst single piece of material, and the flexible member 107 and themirror base 102B are fabricated from a second single piece of material,such as single crystal silicon. The configuration set forth in FIG. 1Ais not intended to limit the scope of the invention in any way. Thus,the use of any configuration that allows the surface of one component(e.g., mirror 102) to contact the surface of another component (e.g.,base 103) during device operation generally falls within the scope ofthe invention. For example, a simple cantilever beam that pivots about ahinge in response to an applied force such that one end of thecantilever beam contacts another surface of the device is within thescope of the invention.

In one aspect, one or more optional landing pads (elements 104A and 104Bin FIG. 1A) are formed on the surface 105 of the base 103. The landingpads are formed, for example, by depositing a metal layer containingaluminum, titanium nitride, tungsten or other suitable materials. Inother configurations, the landing pads may be made of silicon (Si),polysilicon (poly-Si), silicon nitride (SiN), silicon carbide (SiC),copper (Cu), titanium (Ti) and/or other suitable materials.

FIG. 1B illustrates the single mirror assembly 101 in a distorted statedue to the application of an electrostatic force F_(E) created byapplying a voltage V_(A) between the mirror 102 and the electrode 106Ausing a power supply 108. In one aspect, as shown in FIG. 1B, it mayalso be desirable to bias a landing pad (e.g., elements 104A) to thesame potential as the electrode (e.g., element 106A). During typicaloperation, the single mirror assembly 101 is actuated such that themirror 102 contacts the landing pad 104A to ensure that at a desiredangle is achieved between the mirror 102 and the base 103 so thatincoming light “A” is reflected off the surface of the mirror 102 in adesired direction “B.” The deflection of the mirror 102 towards theelectrode 106A due to the application of voltage V_(A) creates arestoring force F_(R) (e.g., moment), due to the bending of the flexiblemember 107. The magnitude of the restoring force F_(R) is generallylimited by the physical dimensions of the flexible member 107, themagnitude of distortion experienced by the flexible member 107 and themechanical properties of the material from which the flexible member 107is made. One should note that the maximum restoring force F_(R) istypically no greater than the torque applied by the electrostatic forceF_(E) that can be generated by the application of the maximum voltageV_(A). To assure contact between the mirror 102 and the landing pad 104Athe electrostatic force F_(E) must be greater than the maximum restoringforce F_(R).

FIGS. 2A-2B are close-up illustrations of a contact region 132A of thedeflected single mirror assembly 101 and the landing pad 104A of FIG.1B. A gas-phase lubricant, representatively illustrated as elements 131,is disposed in the contact region 132A, which is formed between theinteracting components, and a region 132B, which surrounds thecomponents of the single mirror assembly 101 that contact the landingpad 104A, such as mirror 102. Referring to FIG. 2A, as the distancebetween the mirror 102 and the landing pad 104A decreases, theinteraction between the surfaces of these components generally createsone or more stiction forces F_(s) that acts on the mirror 102. When thestiction forces F_(s) equals or exceeds the restoring force F_(R),device failure results, since the mirror 102 is prevented from moving toa different position when the electrostatic force generated by voltageV_(A) is removed or reduced.

As previously described herein, stiction forces are complex surfacephenomena that generally include three major components. The first isthe so-called “capillary force” that is created at the interface betweena liquid and a solid due to an intermolecular force imbalance at thesurface of a liquid (e.g., Laplace pressure differences) that generatesan adhesive-type attractive force. Capillary force interaction in MEMSand NEMS devices usually occurs when a thin layer of liquid is trappedbetween the surfaces of two contacting components. The second majorcomponent of stiction forces is the Van der Waal's force, which is abasic quantum mechanical intermolecular force that results when atoms ormolecules come very close to one another. When device components contactone another, Van der Waal's forces arise from the polarization inducedin the atoms of one component by the presence of the atoms of the secondcomponent. When working with very planar structures, such as those inMEMS and NEMS devices, these types of stiction forces can be significantdue to the size of the effective contact area. The third major componentof stiction forces is the electrostatic force created by the coulombicattraction between trapped charges found in the interacting components.

Referring back now to FIG. 2A, a gas-phase lubricant 131 is disposed inthe contact region 132A between the interacting surface of the mirror102 and the landing pad 104A to reduce the stiction forces createdbetween these two components during device operation. The gas-phaselubricant 131 preferably has an adequate sticking coefficient, oradsorption coefficient, in relation to the relevant component surfaces(here, the surfaces of the mirror 102, surface 105 and landing pad 104A)and therefore forms an adsorbed monolayer 131A (FIG. 3A) on the landingpad 104A. The monolayer 131A advantageously reduces the directinteraction between the mirror 102 and the landing pad 104A and, thus,decreases the likelihood of stiction-related failures. Morespecifically, it is believed that the monolayer 131A of gas-phaselubricant 131 impedes the generation of Van der Waal's forces betweenthe atoms of the mirror 102 and the landing pad 104A and also reducesthe coulombic attraction between the atoms of the mirror 102 and thelanding pad 104A by reducing the potential differences between thesurfaces of these two components. In another embodiment, introducing agas-phase lubricant 131 having a high molecular weight (e.g., >100 amu)may also increase the ability of the monolayer 131A to act as a “buffer”or “bumper” between the mirror 102 and the landing pad 104A, furtherreducing the probability of stiction-related failures. The ability ofthe gas-phase lubricant to act as a “buffer” or “bumper” between theinteracting surfaces may be due to the relatively large size of the gasmolecules. The buffering property of the gas-phase lubricant may bepresent even in the absence of the formation of an adsorbed monolayer.In one aspect, the gas-phase lubricant may also form multiple adsorbedlayers that supplement the lubrication/anti-stiction/anti-wearproperties of the gas-phase lubricant or other added lubricatingmaterials (e.g., self assembled monolayer (SAM) coatings). Referring toFIG. 2A, although the absorbed monolayer of gas-phase lubricant isillustrated as being formed on the landing electrode 104A, it ispossible for an adsorbed monolayer to form alternately on the contractsurface of the mirror 102, or on both the landing electrode 104A and themirror 102. FIG. 3A illustrates the case where an adsorbed monolayer131A of the gas-phase lubricant 131 has formed on the surface 105 of thebase 103 and on all surfaces of the mirror 102, and thus is able toreduce the stiction forces by reducing the interaction of the mirror 102and the landing electrode 104A. FIG. 3B is intended to illustrate a casewhere an adsorbed monolayer of the gas-phase lubricant is not formed,but the gas-phase lubricant 131 acts as a “buffer” (element 131B)between the mirror 102 and the landing electrode 104A, due to thepresence of the gas-phase lubricant between the moving components.

In one embodiment, the surfaces on which the gas-phase lubricant adsorbsis tailored by the careful selection of materials from which the devicecomponents are formed or by performing surface modification steps, whicheither enhance or inhibit the interaction of the surface with thegas-phase lubricant. In one embodiment, the surfaces of the device(e.g., single mirror assembly 101) are modified by exposing them tomicrowaves, UV light, thermal energy, or other forms of electromagneticradiation. In one aspect, all surfaces of the device are exposed to theone or more forms of electromagnetic radiation to modify the surfaceproperties of the exposed surfaces. In another aspect, only definedregions of the device are exposed to the one or more forms ofelectromagnetic radiation to modify the surface properties of theexposed surfaces.

In another embodiment, a “primer,” or organic precursor material, may beselectively deposited on desired surfaces of the device to encourage theformation of a gas-phase lubricant monolayer at these locations. FIG. 3Cillustrates the case where an adsorbed monolayer is preferentiallyformed on the landing electrode 104A, the mirror edge 102C, and part ofthe mirror base surface 102D. FIG. 3C also illustrates the case wherethe gas-phase lubricant also acts as a “buffer” (element 131B) betweenthe surfaces that have an adsorbed monolayer 131A formed thereon, whichmay further help to reduce the interaction of the components, and thusreduce the chance of stiction type failure. The term “adsorbedmonolayer” as used in herein is not intended to limit the scope theinvention described herein, since the mechanism by which gas-phaselubricant interacts with the moving components is very complex and isnot intended to limit the scope of effect of adding a gas-phaselubricant in a region surrounding a device to reducing stiction typefailures. Further, the term monolayer is intended to describe a layerthat is a single molecule thick, as well as a layers that are manymolecules in thickness.

In one embodiment, the gas-phase lubricant 131 is a gas at normal deviceoperating temperatures. Typically, a device may be stored in areas wherethe temperature is between about −30° C. and about 70° C. and operate ata temperature that is within a standard operating temperature range,which is between about 0° C. and about 40° C. In one aspect, thegas-phase lubricant 131 is a gas, or is in a gaseous state, attemperatures preferably greater than about −30° C. In one aspect, thegas-phase lubricant 131 is disposed within a device that is adapted tooperate at a temperature that is within an extended operatingtemperature range, which is between about 0° C. and about 70° C. In oneaspect, the gas-phase lubricant 131 is selected so that it will notdecompose at elevated temperatures, such as temperatures between about300° C. and about 400° C., which are the temperatures that may beexperienced during a typical MEMS or NEMS packaging process. Further, asa gas, the gas phase lubricant easily diffuses around and betweencomponents and thus generally does not require any special processingsteps for the gas-phase lubricant to reliably cover the exposed surfacesto diminish stiction related problems. Further still, upon diffusion ofthe gas phase lubricant between opposing contact surfaces, the gas canimmediately act as a buffer as described previously.

In general, an exemplary gas-phase lubricant has one or more of thefollowing properties. First, an exemplary gas-phase lubricant has a highadsorption coefficient (i.e., large physisorption or chemisorptionenergy) so that the lubricant covers the exposed surfaces of the device,thereby reducing the direct interaction between contacting componentsurfaces during device operation. Second, an exemplary gas-phaselubricant has a low surface energy once disposed on the interactingcomponent surfaces of a device, which reduces the stiction-relatedforces between the components when their surfaces are brought near eachother during device operation. Third, an exemplary gas-phase lubricanthas good lubrication properties to reduce friction forces betweencontacting surfaces. Fourth, an exemplary gas-phase lubricant has a lowviscosity to reduce any retarding force that may adversely affect thedynamic motion of device components during operation. In one aspect, thegas-phase lubricant has a viscosity between about 10 micropoise andabout 100 micropoise. Fifth, an exemplary gas-phase lubricant should notchemically attack or react with the materials from which the variouscomponents of the micromechanical device are made (e.g., silicon,aluminum, glass materials). Sixth, an exemplary gas-phase lubricantgenerally repels water (e.g., hydrophobic) to reduce the capillary-typestiction forces generated between the surfaces of interactingcomponents. Seventh, an exemplary gas-phase lubricant exists in agaseous state at standard temperature and pressure conditions. Eighth,an exemplary gas-phase lubricant exists in a gaseous state at standardtemperature and a pressure above atmospheric pressure. Ninth, anexemplary gas-phase lubricant exists in a gaseous state at standardtemperature and a pressure below atmospheric pressure. Tenth, anexemplary gas-phase lubricant exists in a gaseous state at theconditions under which it is introduced to the components to belubricated. Eleventh, an exemplary gas-phase lubricant exists in agaseous state under the operating conditions of the components to belubricated. Twelfth, an exemplary gas-phase lubricant exists in agaseous state when the components are in a non-standard operatingcondition (e.g., temperature or pressure is not in a desired range).Thirteenth, an exemplary gas-phase lubricant forms a monolayer oncomponents at standard temperature and pressure. Fourteenth, anexemplary gas-phase lubricant forms a monolayer on components under thenormal operating conditions. Fifteenth, an exemplary gas-phase lubricantforms a monolayer on components under non-standard operating conditions.Sixteenth, an exemplary gas-phase lubricant repairs a thin film layer ona component under normal operating conditions. Seventeenth, an exemplarygas-phase lubricant repairs a thin film layer on a component undernon-standard operating conditions of the component. Other factors thatmay be considered when selecting an appropriate gas-phase lubricant arewhether the lubricant is non-toxic and whether the lubricant has a lowmaterial cost. In another aspect, an exemplary gas-phase lubricant mayalso be non-polar, which tends to mitigate Van der Waal-type stictionforces formed between the surfaces of interacting components.

In configurations where the gas-phase lubricant is used in opticaldevices (e.g., digital spatial light modulators) an exemplary gas-phaselubricant may exhibit the following additional properties: (1) thegas-phase lubricant does not absorb the wavelengths of the incident orreflected optical radiation, (2) the gas-phase lubricant does notfluoresce due to the exposure to the incident optical radiation, and (3)the gas-phase lubricant does not breakdown due to the presence of theincident or reflected radiation (e.g., UV wavelengths).

In some configurations where the gas-phase lubricant is used in amicromechanical device an exemplary gas-phase lubricant may exhibit thefollowing additional electrical properties: (1) the gas-phase lubricantdoes not ionize in an electric field up to about 300 Volts/μm, and (2)the gas-phase lubricant has good electrical insulating properties (e.g.,high dielectric constant or permittivity). In one aspect, a gas-phaselubricant is selected that has a higher dielectric constant than typicalgases used in conventional MEMS components, for example, nitrogen, air,argon, helium, or combinations thereof. The use of a gas-phase lubricantthat has a higher dielectric constant can be beneficial since it canallow the circuit capacitance and maximum allowable applied bias V_(A)to increase and, thus, allows the maximum restoring force F_(R) to beincreased. One will note that capacitance, C=∈_(o)∈_(r)A/d, where∈_(o)=permittivity of free space (constant), ∈_(r)=dielectric constantof the gas-phase lubricant, A=area of electrodes and d=distance betweenelectrodes. As previously described, by redesigning the flexible member107 to increased restoring force F_(R), the probability that stictionproblems will arise will be reduced, since a larger stiction force wouldbe required to cause device failure.

In various embodiments, a suitable gas-phase lubricant may be ahaloalkane, sulfur hexafluoride (SF₆), silicon tetrafluoride (SiF₄), orvarious combinations thereof. Some haloalkanes that may be usefulinclude perfluorocarbons (C_(x)F_(y)), such as perfluorocyclobutane(c-C₄F₈), hydrofluorocarbons (H_(x)C_(y)F_(z)) and chlorofluorocarbons(CFCs). Perfluorocyclobutane, also known as octafluorocyclobutane, andsulfur hexafluoride have many advantages since they can easily bepurchased in a pure form and generally do not react with most materials.As previously mentioned, selecting a fluorinated gas-phase lubricantthat has a molecular weight greater than about 100 amu may be desirableto ensure that it displaces typical atmospheric contaminants (e.g.,air), it acts as a buffer between the surfaces of contacting components,and it can adsorb on the surfaces of the contacting components.

Generally, gas-phase lubricants have several advantages overconventional solid and liquid lubricants. These advantages include, butare not limited to, the following: (1) gas-phase lubricants diffuse atrates that are orders of magnitude higher than the rates at whichconventional solid or liquid lubricants diffuse, which allows more rapidcoverage of exposed surfaces created during the actuation of amicromechanical device, (2) gas-phase lubricants generally have a lowviscosity, which reduces the possibility of the lubricant interferingwith the dynamic motion of the moving components of a micromechanicaldevice, (3) gas-phase lubricants are generally less expensive, and (4)gas-phase lubricants generally do not require additional, expensiveprocessing steps to deposit and/or retain the lubricant materials withina micromechanical device. Also, in one aspect of the invention, sincethe gas-phase lubricant is disposed in the region 132B that surroundsthe mirror 102, a ready supply of the lubricant is available toreplenish “damaged,” desorbed or broken down lubricant material, whichmay result during operation of the micromechanical devices.

FIG. 2B is a close-up illustration of the deflected single mirrorassembly 101 of FIG. 1B that has been coated with a liquid or solidlubricant material 135. Also shown is the gas-phase lubricant 131disposed in the region 132A between the interacting surfaces of themirror 102 and the landing pad 104A. In this embodiment, the solid orliquid lubricant material 135 can be used to modify the surfaces of themirror 102 and the landing pad 104A to reduce their respective surfaceenergies, thereby further decreasing the likelihood of stiction-relatedfailures. More specifically, adding the lubricant coating 135 may makethe surfaces more hydrophobic, which reduces capillary-type stictionforces. Exemplary solid or liquid lubricants may include organicmaterials or other similar surface modifying component(s), such asself-assembled-monolayer (SAM) materials. As is well-known, SAMsgenerally include a single layer of molecules deposited on a substratesurface by simply adding a solution of the desired molecule onto thesubstrate surface and washing off the excess. Examples of useful SAMmaterials include, but are not limited to organosilane type compounds(e.g., octadecyltrhichlorosilane (OTS), perfluorodecyltrichlorosilane(FDTS)).

The gas-phase lubricant 131 may be used to reduce degradation of thesolid or liquid lubricant coating 135, such as a SAM layer, by reducingthe amount of wear experienced by the lubricant coating 135 duringoperation. As a general matter, the lubricating properties of thegas-phase lubricant 131 and/or the adsorption of the gas-phase lubricant131 on the surfaces coated with the solid or liquid lubricant tend toreduce the amount of wear experienced by the solid or liquid lubricantcoating 135 during operation. Moreover, the gas-phase lubricant 131 alsomay act to “heal” regions of the lubricant coating 135 that are damagedduring device operation. For example, when regions of the lubricantcoating 135 are worn away by the continual contact or interaction of themoving device components, the high diffusion rate of the gas-phaselubricant 131 enables the gas-phase lubricant 131 to rapidly diffuse tothose regions and replace the damaged portions of the lubricant coating135.

FIGS. 4A-4D are intended to schematically illustrate a cross-sectionalview of a single MEMS device, such as a single mirror assembly 101, atdifferent stages of its life. FIGS. 4A-4D are also intended toillustrate one example of how a damaged lubricant coating 135 can be“healed” by use of the gas-phase lubricant. FIG. 4A illustrates across-sectional view of a single mirror assembly 101 that has acontinuous lubricant coating 135 deposited over the exposed surfaces.FIG. 4B is intended to illustrate how the lubricant coating 135 maybecome damaged due to the interaction of the various components (e.g.,elements 102 and 104A). As shown in FIG. 4B, the lubricant coating 135may become displaced or damaged due to the contact between theinteracting surfaces, which can leave exposed regions (element “G” inFIG. 4C) of the underlying surfaces. FIG. 4C illustrates across-sectional view of a single mirror assembly 101 in its undeflectedstate that has a lubricant coating 135 coating that has become damagedand is “healed” due to the adsorption of the gas-phase lubricant in theexposed regions “G.” FIG. 4D is intended to illustrate how the gas-phaselubricant can help reduce the interaction between the interactingsurfaces that have a damaged lubricant coating 135 by the adsorption orbuffering effect of the gas-phase lubricant in the exposed regions “G”.The adsorption or buffering effect of the gas-phase lubricants can thushelp increase the longevity of devices that have a lubricant coating 135disposed over the interacting regions of the device.

In one embodiment, the components in the micromechanical device thatcontact one another during device operation may be processed using aconventional hexamethyldisilazane (HMDS) treatment process to form thelubricant coating 135 prior to disposing the gas-phase lubricant in theregion surrounding the components. As is well-known, an HMDS processgenerally includes bringing a gas containing a vaporized HMDS materialin contact with silicon containing component surfaces, causing asilylation process to occur on the component surfaces, which generallyreduces the surface energies of the exposed component surfaces.

An example of other types of devices that may receive a benefit from thevarious embodiments of the invention described herein is shown in FIGS.5A-5B. FIG. 5A illustrates a cross-sectional view of a single pixel 20found in a digital micromirror device (DMD) spatial light modulator inits undeflected state that has a gas-phase lubricant 131 disposed withinthe region 21 that surrounds the pixel 20. Adding the gas-phaselubricant in this fashion reduces stiction problems. The pixel 20 maygenerally contain a mirror 30 (e.g., similar to element 102 in FIG. 1A),support posts 34, a yoke 32, mirror address electrodes 50 and 52, andaddress electrodes 26 and 28. FIG. 5B illustrates a cross-sectional viewof the pixel 20 in its deflected state after a sufficient bias has beenapplied between the address electrode 28 and the yoke 32 and between theelevated electrode 52 and the mirror 30. In this configuration, thegas-phase lubricant 131 disposed around a pixel 20 reduces the chancesthat substantial stiction forces will arise between the yoke tip 58 andthe address electrode 28 by reducing the interaction of these surfaces,as discussed above. A specific example of a single-pixel type devicethat may benefit from the teaching of the invention set forth herein isfurther described in U.S. Pat. No. 5,771,116, filed Oct. 21, 1996.

Another example of a MEMS device that may benefit from the use of thegas-phase lubricant 131 is shown in FIGS. 5C-5D. This type of MEMSdevice is a moveable mirror device. FIG. 5C illustrates across-sectional view of a micro-mirror plate 210 that is in itsundeflected state that has a gas-phase lubricant 131 disposed in theregion 284 that surrounds the micro-mirror plate 210 (e.g., similar toelement 102 in FIG. 1A). Again, adding the gas-phase lubricant 131reduces stiction-related problems created when the micro-mirror plate210 interacts with other surfaces. The MEMS moveable mirror device maygenerally contain the micro-mirror plate 210, electrodes 282 and 283, ahinge support 263, a shallow via contact 241 for providing a rotationalaxis, a wafer 281, and mirror stops 270. FIG. 5D illustrates across-sectional view of the micro-mirror plate 210 in its deflectedstate after a sufficient bias has been applied between the electrode 283and the micro-mirror plate 210 by a power supply (not shown). In thisconfiguration the gas-phase lubricant 131 disposed around themicro-mirror plate 210 reduces the chances that substantial stictionforces will arise between the micro-mirror plate 210 and the glasssubstrate 280 by reducing the interaction of the surfaces, as discussedabove. A specific example of a moveable micro-mirror-type device thatmay benefit from the teaching of the invention set forth herein isfurther described in U.S. Pat. No. 6,960,305, filed Mar. 28, 2003.

FIG. 6 illustrates a device package 200 containing an array of singlemirror assemblies 101 positioned within a processing region 113 (oroperating region), according to one embodiment of the invention. Asshown, the processing region 113 is formed between a lid assembly 111that is sealably coupled to a substrate 203 by use of a sealing member112. The processing region 113 is filled with gas-phase lubricant thatsurrounds each of the individual mirror assemblies 101 disposed withinthe processing region 113. The processing region 113 may be filled withthe gas-phase lubricant either prior to having the lid assembly 111sealably coupled to the substrate 203, or may be filled via a fill linewith access to the interior of the processing region 113. In one aspect,enough gas-phase lubricant is added to the processing region 113 so thatthe pressure within the processing region 113 is greater thanatmospheric pressure. Such a configuration is useful since it reducesthe likelihood that atmospheric contaminants will leak into theprocessing region 113 over the lifetime of the device. In oneembodiment, the gas-phase lubricant is disposed within the processingregion 113 when the lid assembly 111 is bonded and hermetically sealedto the substrate 203 during device fabrication. In another aspect, thegas-phase lubricant is added to the processing region 113 so that thepressure within the processing region 113 is less than atmosphericpressure.

In one aspect, the lid assembly 111 contains an optically transparentregion 111A made of a display grade glass (e.g., Corning® Eagle 2000™)and a standoff element 111B made of a suitable material such as silicon.In general, the sealing member 112 can be an elastomeric element or abonded region formed by bonding the lid assembly 111 to the substrate203. Typical bonding processes include anodic bonding (e.g.,electrolytic process), eutectic bonding, fusion bonding, covalentbonding, and/or glass frit fusion bonding processes. Examples ofexemplary device packages 200 and processes of forming the devicepackages that may be used with one or more embodiments of the inventiondescribed herein are further described in the following commonlyassigned U.S. patent application Ser. No. 10/693,323, filed Oct. 24,2003, U.S. patent application Ser. No. 10/902,659, filed Jul. 28, 2004,and U.S. patent application Ser. No. 11/008,483, filed Dec. 8, 2004.

In one embodiment, the substrate 203 contains an array of MEMS that areformed on a surface 203A of the substrate 203. An example of a method offorming an array of MEMS devices on the substrate 203 is furtherdescribed in the co-pending U.S. patent application Ser. No. 10/756,936,filed on Jan. 13, 2004. In another embodiment, the substrate 203 isformed from two major components that include, but are not limited to, adevice substrate (element 352 in FIG. 7A) that includes the array ofMEMS devices formed thereon, and a package base (element 350 in FIG.7A). In such a configuration, the package base 350 is generally aseparately machined component that is adapted to receive the devicesubstrate 352 and be sealably connected to the lid assembly (element 351in FIG. 7A) to form an enclosed processing region 113 around the arrayof MEMS devices formed on the device substrate 352.

Device Package Forming Processes

FIGS. 7A-7D and 8A-8E schematically illustrate the final stages of theprocess of forming an exemplary device package 200 that contains agas-phase lubricant. More specifically, FIGS. 7A-7D illustrate a chiplevel device packaging process in which a gas phase lubricant isdisposed in the processing region 113 of the formed device and FIGS.8A-8D illustrate a wafer level device packaging process in which a gasphase lubricant is disposed in the processing region 113 of the formeddevices. FIGS. 9 and 10 illustrate a packaging method 600 that has aseries of method steps (e.g., elements 602-614) for forming theexemplary device package 200 that has a gas phase lubricant disposedwithin the processing region 113.

Each of the methods described in FIGS. 9 and 10 include a bondingprocess step to form a sealed processing region 113 around themicromechanical device(s). In one embodiment, the bonding process isperformed in a bonding chamber assembly 300 (FIGS. 7A-7D and 8A-8D) thatgenerally contains a bonding chamber 301, an exhaust system 303, a fluiddelivery system 302, a heating device (not shown) and an actuator (notshown) that is adapted to position all of the device package 200components so that the process of sealably bonding all of the majorsubassembly components together to form the device package 200 can becompleted. In one aspect, the bonding chamber 301 is a conventionalvacuum processing chamber that is adapted to form the device package 200in a vacuum, atmospheric and/or elevated pressure environment. In oneaspect, the exhaust system 303 contains one or more vacuum pumps thatare adapted to pump down the chamber processing region 304 to a desiredvacuum state during one or more of the processing steps. In one aspect,the exhaust system 303 is also be able to receive, reclaim and/orexhaust the various process gases injected into the chamber processingregion 304. In one aspect, the fluid delivery system 302 contains aplurality of fluid sources that may be used during the packaging method600. For example, as illustrated in FIG. 7A, the fluid delivery system302 may contain a first fluid source 302A that is adapted to deliver agas-phase lubricant and a second fluid source 302B that is adapted todeliver one or more components that are used to deposit a lubricantcoating 135, such as a SAM layer.

Referring now to FIGS. 9 and 10, in step 602, all of the majorsubassemblies and components are formed so that the final packagingsteps can be performed. Thus, step 602 occurs prior to the stepsillustrated in FIGS. 7A and 8A (i.e., prior to the final steps ofsealably forming the device package 200). The major subassemblies aregenerally formed using conventional manufacturing techniques up to thepoint where the step of bonding two or more components together, such asbonding the lid assembly 111 to the substrate 203, is the only processstep before the processing region 113 is sealably formed around the MEMSdevice. Examples of various processing steps that may be completed toform the major subassemblies prior to forming the device package 200 arefurther described in the following commonly assigned U.S. patentapplication Ser. Nos. 10/693,323, 10/902,659, and 11/008,483. As setforth in these applications, some of the steps used to form the majorsubassemblies may include, but are not limited to, using one or moreconventional semiconductor processing techniques to form the variousMEMS devices, performing the machining and preparation steps to form thelid assembly 111, and forming one or more wire-bonding steps to connectthe MEMS device to the various external leads.

Referring specifically to FIG. 9, in step 604, the various majorsubassemblies are positioned in the bonding chamber 301 of the bondingchamber assembly 300 so that the major subassemblies can be bondedtogether using conventional bonding techniques, as described below instep 612, to form the device package 200. Referring to FIG. 7A, in oneembodiment, the major device package 200 assemblies consist of two majorcomponents: a lid assembly 351 (e.g., similar to element 111 discussedabove) and a package base 350 that has a device substrate 352 mounted init. In this configuration, each of the major components is positioned inthe chamber processing region 304 of the bonding chamber 301 so that theelement is in contact, or communication, with the processing region 304.In general, the device substrate 352 has one or more micromechanicaldevices formed on it by use of conventional manufacturing techniques.

In step 606, the bonding chamber 301 is pumped down to a vacuum stateand/or the bonding chamber 301 is purged with clean and dry gas. In oneaspect, the bonding chamber is pumped down to a pressure between about10⁻⁶ Torr and about 10⁻³ Torr and maintained at this pressure for adesired period of time to assure that the device package 200 has beencompletely outgassed and thus is free of any residual water or othercontaminants. In another aspect, the bonding chamber 301 is maintainedat a pressure near atmospheric pressure while a flow of a high-purity,clean and dry gas is delivered from the fluid delivery system 302 to theexhaust system 303. The flow of a high-purity, clean and dry gas throughthe chamber processing region 304 reduces the partial pressure of waterand other contaminants in the bonding chamber 301. Typical high-purity,clean and dry gases may include, but are not limited to, inert gasessuch as argon (Ar), Nitrogen (N₂), and helium (He). These types of gasescan be purchased in an electronic or VLSI grade that has a purity levelof at least ≧99.999%. In yet another aspect, a one or more pump down andthen backfill with a high-purity, clean and dry gas steps are performedto more rapidly reduce the time required to remove the unwantedcontaminants (e.g., water) from the device package 200 components andthe bonding chamber 301.

In step 608, an optional bakeout out step is performed by heating thebonding chamber 301 and device package 200 components to an elevatedtemperature, while the bonding chamber 301 is maintained at a vacuumpressure (<760 Torr) or in an environment of a clean and dry gas tofurther remove any contaminants from the chamber processing region 304.In one aspect, the bonding chamber 301 and device package 200 componentsare heated to a temperature of about 150° C. for a period of timebetween about 30 and about 100 minutes to assure the removal of anyunwanted contaminants. In one example, the temperature of the bondingchamber 301 and device package 200 components are slowly increased tothe bakeout temperature at a rate of about 15° C./minute. The bondingchamber 301 and device package 200 components may be heated by use ofconventional radiant heat lamps (not shown), conventional resistiveheaters (not shown) or other similar devices positioned in the chamberprocessing region 304 or mounted on the external walls of the bondingchamber 301.

In step 610, the gas-phase lubricant is backfilled into the chamberprocessing region 304 until a desired pressure is achieved. In oneaspect, the gas-phase lubricant is added until the pressure in thechamber processing region 304 is in a range between about 700 Torr andabout 800 Torr. Referring to FIG. 7B, the gas-phase lubricant 131 isdelivered to the chamber processing region 304 from the first fluidsource 302A until the desired pressure is achieved. In one aspect of thepackaging method 600, prior to performing step 610, pumping the chamberprocessing region 304 to a high vacuum state (e.g., 10⁻⁵ Torr) tofurther assure that any residual gases and contaminants are removed. Inone embodiment, the deposition of the lubricant coating 135 is completedprior to performing step 610.

Referring again to FIG. 7C, in step 612, the lid assembly 351 is bondedto the package base 350 so that the device substrate 352 and gas-phaselubricant are trapped in the formed processing region 113 of the devicepackage 200. Typical bonding processes may include anodic bonding (e.g.,electrolytic process), eutectic bonding, fusion bonding, covalentbonding, and/or glass frit fusion bonding processes. After the lidassembly 351 is bonded to the package base 350, the gas-phase lubricant131 can be removed from the chamber processing region 304 (e.g., FIG.7D), bonding chamber 301 can be vented, and then the device package 200can be removed from the bonding chamber 301 so that any furtherprocessing steps that are needed to form a fully functional device maybe performed on the device package 200.

One should note that gas-phase lubricants generally do not need to be“activated” during the device package forming processes. By contrast,the activation process is usually necessary when forming a device thatuses conventional solid and liquid phase lubricants. Typically,activation processes require the use of high temperature (e.g., 300 to400° C.) activation steps to cause the solid or liquid lubricant(s) tobond to desired components and become an effective lubricant. Thetemperatures used to perform the activation process(es) are usuallyequivalent to the highest temperatures that the device packagecomponents experience during the device packaging process. Again, insharp contrast, the gas-phase lubricant does not require theseactivation steps and thus allows the flexibility of using lowertemperature sealing materials and processes, which may make the devicepackages 200 less expensive and easier to manufacture. Moreover, in oneaspect, due to the anti-stiction and anti-wear properties of thegas-phase lubricant the activation process steps are not used and thusthe device packaging process can be performed at temperatures less thanabout 250° C.

Wafer Level Packaging

FIGS. 8A-8D illustrate a wafer level device packaging process in which agas phase lubricant is disposed in the processing region 113 of theformed devices following the steps described in FIG. 10. The methodsteps 602 through 612 are generally the same as described above inconjunction with FIG. 9 except a wafer level packaging process is usedto eventually form multiple device packages 200 (FIG. 8E). Referring toFIGS. 8A and 10, in step 602, all of the major subassemblies (e.g.,elements 451 and 452) are formed so that the final packaging steps canbe performed. The major subassemblies are generally formed usingconventional manufacturing techniques to the point where the step ofbonding two or more components together is the only process step left toperform before the processing region 113 is sealably formed around theMEMS devices. As noted above, an example of various processing stepsthat may be completed to form the major subassemblies prior to formingthe device package 200 are further described in the following commonlyassigned U.S. patent application Ser. Nos. 10/693,323, 10/902,659, and11/008,483.

In step 604, the various major subassemblies are positioned in thebonding chamber 301 of the bonding chamber assembly 300 so that themajor device package 200 assemblies can be brought into contact andbonded together using conventional bonding techniques. Referring to FIG.8A, the major device package 200 assemblies generally consist of twomajor components: a lid assembly 451 (e.g., similar to element 111discussed above) and a substrate 452 that has a plurality of MEMS arrays453 formed on it. In this configuration, each of the major componentsare positioned in the chamber processing region 304 of the bondingchamber 301 so that the each element is in contact, or communication,with the processing region 304. In general, the MEMS arrays 453 formedon the substrate 452 generally contain a plurality of micromechanicaldevices that are formed by use of conventional semiconductormanufacturing techniques.

In step 606, the bonding chamber 301 is pumped down to a vacuum stateand/or the bonding chamber 301 is purged with clean and dry gas, asdescribed above. In step 608, an optional bakeout out step is performedby heating the bonding chamber 301 and device package 200 components toan elevated temperature while the chamber processing region ismaintained at a vacuum pressure (<760 Torr) or at a pressure nearatmospheric pressure that has a low partial pressure of contaminants(e.g., water), as described above. In step 610, the gas-phase lubricantis backfilled into the chamber processing region 304 until a desiredpressure is achieved, as described above. In one embodiment, thedeposition of the lubricant coating 135 is completed prior to performingstep 610.

In step 612, referring again to FIG. 8C, the lid assembly 451 is bondedto the substrate 452 so that the gas-phase lubricant is trapped in theformed processing regions 113 around each of the MEMS arrays 453 in eachof the device packages 200. Typical bonding processes may include anodicbonding (e.g., electrolytic process), eutectic bonding, fusion bonding,covalent bonding, and/or glass frit fusion bonding processes. After thelid assembly 451 is bonded to the substrate 452, the gas-phase lubricant131 can be removed from the chamber processing region 304 (e.g., FIG.8D), bonding chamber 301 can be vented, and then the device package 200can be removed from the bonding chamber 301.

In step 614, the bonded lid assembly 451 and substrate 452 are thencleaved, sawed or diced to form multiple device packages 200 so that anyfurther processing steps that need to be completed to form a fullyfunctional device may be performed on the device package 200. In oneembodiment, the individual dies are separated (e.g., cleaved, sawed ordiced) by cutting the substrate into dies using a diamond saw. In analternative embodiment, the dies are separated by scribing the substrate451 using a diamond scribe. In an embodiment of the invention in whichthe substrate is a silicon wafer, the die separation is performed bysawing the silicon substrate with a rotating circular abrasive sawblade. As shown in FIGS. 8A-8E three device packages 200 are formed sothat the gas-phase lubricant (element 131) is positioned in theprocessing region 113 to reduce stiction type failures.

FIG. 11A is cross-sectional view of device package that has getters 360and a gas-phase lubricant 131 positioned in the processing region 113 ofthe device package 200. In this configuration the formed device maybenefit from the use of a solid or liquid lubricant that is retained andslowly leached from the getters 360 and also the rapid “healing” and/orbuffering effect of the gas-phase lubricant. As noted above getters aregenerally used to trap any moisture found in the processing region 113and also slowly release the liquid lubricant. However, by following theprocesses described above in FIGS. 9 and 10 to form a device package 200and/or the fact that most of the exemplary gas-phase lubricantsdiscussed above can be delivered in a pure or “dry” form, the need forthe moisture trapping function of the getter materials is generally notneeded. Further, since the gas-phase lubricant can placed in theprocessing region 113 of the device package at a pressure greater thanatmospheric pressure the chance of atmospheric contamination fromentering the processing region 113 from the outside of the devicepackage is greatly reduced, which also reduces the need for the getters360.

Moreover, since the exemplary gas-phase lubricants are effective inreducing stiction related problems the liquid lubricants areun-necessary. Therefore, in one aspect of the invention, a devicepackage 200 containing only gas-phase lubricants is used with no getters360 and no liquid lubricants. One advantage of removing the need for theoften expensive getters 360 is the fact that the size of the devicepackage can be much smaller than conventional device packages thatcontain getters. FIG. 11B illustrates a cross-sectional view of a devicepackage 200 that contains only a gas-phase lubricant 131. Since thespace in the processing region 113 that was taken up by the getters 360is not needed the device package can be made much smaller in size thanconventional device packages (see FIG. 11A). The reduction in the devicepackage size will reduce the manufacturing and piece part costs, thusmaking the device package forming process much more cost effective andcompetitive.

FIG. 12 illustrates a device package 201 that contains an array ofsingle mirror assemblies 101 and gas-phase lubricant source assembly 121that is coupled to the processing region 113, according to oneembodiment of the invention. The gas-phase lubricant source assembly 121generally includes a gas-phase lubricant source 118 and a gas-phaselubricant collection device 119 that are fluidly coupled to theprocessing region 113 so that a flow of the gas-phase lubricant (element“C”) can be continuously or intermittently delivered to the processingregion 113 as desired. As shown, the gas-phase lubricant is deliveredfrom the gas-phase lubricant source 118 through an inlet tube 116 thatis sealably connected to the substrate 203, through an inlet gas port115 formed in the substrate 203, into and through the processing region113, out the exit gas port 120 formed in the substrate 203, through theoutlet tube 117 that is sealably connected to the substrate 203, andinto the gas-phase lubricant collection device 119. The gas-phasecollection device 119 may be simple vessel adapted to collect thegas-phase lubricant, or the collection device 119 may be a conventionalexhaust or recycling system.

Experiments have shown that the gas-phase lubricant may be injected intothe processing region 113 of the device package 201 to release devicecomponents that have become inoperable due to stiction-type forcesgenerated during device operation. In one aspect, the gas-phaselubricant may be injected into the processing region 113 until a desiredconcentration of gas-phase lubricant has been achieved. In anotheraspect, a flow of gas-phase lubricant may be delivered through theprocessing region 113 for a set period of time or until the devicecomponents become operable once again. In either case, introducing thegas-phase phase lubricant appears to reduce the stiction forces F_(s)between device components enough to allow the restoring force F_(R) toreturn the moving component (e.g., the mirror assembly 101 of FIG. 1B)to its un-actuated positions. In another embodiment, a process may beemployed which allows one or more devices that have failed due tostiction to become usable again by allowing the inoperable components toremain idle in the gas-phase lubricant for a period of time. In thisscenario, the gas-phase lubricant already present within the processingregion 113 is allowed to interact with the inoperable components tolower the stiction forces F_(s) enough to allow the restoring forcesF_(R) to move the components back to their un-actuated positions.

The use of the gas-phase lubricant has many benefits when compared toliquid lubricant containing devices, which include reduced materialcost, reduced manufacturing cost, reduced device complexity, and anincreased ability to rapidly “heal” exposed regions between interactingcomponents, to name just few benefits. Another benefit of using agas-phase lubricant is due to its ability to help release inoperablecomponents while they are still in use. Various processing steps can beused to release inoperable components using conventional liquidlubricants, but these processing steps require that the affected devicebe taken out of service so that the device can be immersed in the liquidlubricant. These added steps to help release inoperable components whenusing liquid or solid lubricants is wasteful, time consuming and costly,due to the down time of the system using the failed component and theadded processing steps. Further, liquid lubricants can leave a residuethat will foul the device.

In one embodiment, the gas-phase lubricant may be delivered to theprocessing region 113 only when the MEMS or NEMS device is operational(i.e., component parts are moving) to reduce the overall amount ofgas-phase lubricant used. In another aspect, the gas-phase lubricant maybe delivered to the processing region 113 at a predefined intervalduring device operation to regularly replenish or refresh the gas-phaselubricant in the processing region 113.

The systems and techniques disclosed herein advantageously use agas-phased lubricant to lubricate, reduce stiction-related forces,and/or provide anti-wear protection between contacting surfaces ofmicromechanical devices, such as MEMS devices, NEMS devices. Among otherthings, gas-phase lubricants diffuse at rates that are orders ofmagnitude higher than the diffusion rates of conventional solid orliquid lubricants diffuse. A higher diffusion rate enables a gas-phaselubricant to be self-replenishing, meaning that gas-phase lubricants canquickly move back into a contact region after being physically displacedfrom the region by the contacting surfaces of the micromechanical deviceduring operation. Consequently, gas-phase lubricants are more reliablethan conventional solid or liquid lubricants in preventingstiction-related device failures. Further, gas-phase lubricants and waysto replenish these lubricants may be included in device package designswithout introducing costly fabrication steps or substantially increasingoverall design complexity. Thus, gas-phase lubricants provide areliable, cost-effective way to reduce stiction-related forces in MEMSor NEMS devices relative to conventional solid or liquid lubricants.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of operating a micromechanical device comprising: biasingone or more electrodes, wherein biasing the one or more electrodescauses a moveable component having a first contact surface to interactwith a second contact surface; biasing the one or more electrodesrepeatedly until a stiction force prevents the first contact surfacefrom being separated from the second contact surface; and separating thefirst contact surface from the second contact surface by exposing thefirst and second contact surfaces to a gas-phase lubricant.
 2. Themethod of claim 1, wherein the gas-phase lubricant is a gas containing ahaloalkane.
 3. The method of claim 1, wherein the gas-phase lubricant isselected from a group consisting of sulfur hexafluoride, silicontetrafluoride and perfluorocyclobutane.
 4. The method of claim 1,wherein the gas-phase lubricant is a fluorinated compound that has amolecular weight greater than about 100 amu.
 5. The method of claim 1,wherein the moveable component comprises a mirror.
 6. The method ofclaim 1, wherein the micromechanical device is an optical imageprocessor or a spatial light modulator.